Various damping devices can be used in connection with turbine engines to suppress certain undesired frequencies of dynamics including the frequency band known as screech (1000–5000 Hz). Such high frequency dynamics can result from, for example, burning rate fluctuations inside the combustor section of the turbine. Without a damping device, such frequencies can quickly destroy combustor hardware. Thus, one or more damping devices 10 can be associated with the combustor section 12 of a turbine engine, as shown in FIG. 1. One commonly used damping device 10 is a resonator.
FIGS. 2–5 show one example of a resonator 14 known as a Helmholtz resonator. Generally, the resonator 14 provides a closed cavity 16 defined by a plate 18 having a plurality of inlet openings 20 therein and at least one side wall 22 extending about the periphery of the plate 18. The plate 18 can have any of a number of configurations including substantially rectangular, oval, circular, polygonal or combinations thereof. In addition, the resonator plate 18 can be flat or it can be curved.
The side wall 22 can be formed from a single continuous piece with the resonator plate 18 or it can be made of one or more separate side walls. For example, when the plate 18 is rectangular, there can be four side walls 22 extending from each side of the plate 18. In such case, the side walls 22 can be attached to the outer periphery of the plate 18 and to each other where two walls abut. The side wall 22 can extend substantially perpendicularly away from the resonator plate 18; alternatively, the side wall 22 can taper outwardly from the periphery of the resonator plate 18. The openings 20 in the resonator plate 18 can have any of a number of conformations such as circular, oval, rectangular, triangular, and polygonal.
As shown in FIG. 2, one or more resonators 14 can be secured to and about the outer periphery of a combustor component 24, such as a liner or transition, in any of a number of manners including by welding or brazing. The combustor component 24 can include a plurality of openings 26 through its thickness; the resonator 14 can be attached to the component 24 such that the openings 26 in the combustor component 24 are enclosed by the resonator 14. The combustor component 24 can define one side of the closed cavity 16 of the resonator 14.
Flow can enter the resonator 14 through the openings 20 in the resonator plate 18. The flow can then be reacted by the volumetric stiffness of the closed cavity 16, producing a resonance in the velocity of the flow through the holes 20. This flow oscillation has a well-defined natural frequency and provides an effective mechanism for absorbing acoustic energy. Further, the flow entering the resonator 14 can be used to impingement cool the surface of the combustor component 24, before the flow exits through the holes 26 in the component 24. In addition to the above example, additional resonator configurations are disclosed in U.S. Pat. No. 6,530,221 B1 (“the '221 patent”), which is incorporated herein by reference. The '221 patent discusses the basic resonator operation in greater detail.
Existing resonator design techniques assume a fixed pressure drop across the resonator 14 from the outer side 28 (i.e., the resonator plate 18) to the inner side 30, such as the combustor component 24 (see FIG. 4). Design parameters requiring specification include resonator volume, mass flow through the device and pressure ratio across the inner and outer walls of the resonator. Given this assumption and these parameters, a resonator 14 can be designed to provide a desired level of damping and frequency response. However, if the actual conditions vary from the assumed conditions, the resonator may not perform as designed, which in turn can detrimentally affect the performance of the combustor.
The operating environment of a turbine engine can expose resonators to heavily non-uniform flow and pressure environments. For example, the air flow entering the combustor section is non-uniform, and when this non-uniform flow is combined with the irregular geometries of the neighboring components, a complex flow pressure field develops. Further, the resonators themselves can restrict flow depending on their size. Such restriction can accelerate the flow and diminish the static pressure over the resonators, which typically changes the pressure drop from the design assumption. Moreover, if such non-uniformities must be accounted for in the design, the design of the resonator can become significantly complicated.
Thus, one object according to aspects of the present invention is to provide a resonator configured to deliver a more predictable pressure field to the resonator, even in heavily non-uniform fluid flow environments, so as to allow the resonator to perform as it was designed. Another object according to aspects of the present invention is to provide a resonator configuration that can increase the pressure drop available across the resonator. Still another object according to aspects of the present invention is to provide a resonator design that can even the pressure impinging on the outer surface of the resonator. Yet another object according to aspects of the present invention is to provide a resonator design that facilitates the use of computational tools to predict pressures produced so that these pressures can be relied on in the design process. These and other objects according to aspects of the present invention are addressed below.